The polymerase chain reaction (PCR) can be used to detect small quantities of hepatitis B virus (HBV) DNA, generally by testing for one or two gene sequences, in liver and serum from patients without detectable markers of HBV. It is sometimes necessary to distinguish the detection of HBV DNA from false-positive results due to contamination by carry-over of previously amplified PCR products. Occasional use of "multi-target" PCR using primer sets for portions of the three HBV genes, C, S, and X, simultaneously can verify the lack of contamination by carry-over and enhance the accuracy of PCR.